Method for the estimation of data units transmitted in a radio block via a radio channel and receiving station

ABSTRACT

The invention relates to a method for estimating data units (d 11 , d 12 , d 13 , d 14 , d 21 , d 22 , d 23 , d 24 ) transmitted in a radio block (d) via a radio channel. Based on the transmitted data units (d 11 , d 12 , d 13 , d 14 , d 21 , d 22 , d 23 , d 24 ), a signal sequence (S) is received by a receiving station (BS). The components of the received signal sequence (S) are assigned in the temporal sequence of the reception thereof to at least one first and one second signal block (X 1 , X 2 , X 3 ) and are processed in blocks. The signal blocks (X 1 , X 2 , X 3 ) overlap in such a manner that at least one component of the received signal sequence belongs to the two signal blocks (X 1 , X 2 , X 3 ) and estimation values for the transmitted data units (d 11 , d 12 , d 13 , d 14 , d 21 , d 22 , d 23 , d 24 ) are determined based on the components of both signal blocks (X 1 , X 2 , X 3 ).

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on and hereby claims priority to PCTApplication No. PCT/EP2004/050709 filed on May 5, 2004 and GermanApplication No. 10326810.3 filed on Jun. 13, 2003, the contents of whichare hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The invention relates to a method for estimating data units transmittedin a radio block via a radio channel, together with a correspondingreceiving station.

In radio communication systems, data (for example speech, image data orother data) is transmitted between a base station and a mobile stationvia a radio interface, using electromagnetic waves. In doing so, theelectromagnetic waves are radiated with a carrier frequency which lieswithin a frequency band provided for the system concerned.

The basic principle of multi-carrier methods relates to dividing up highbit-rate data streams into a number of streams with a lower bit-rate.These streams with the lower bit-rate are transmitted simultaneouslyover a number of sub-carriers. For this transmission, inter-symbolinterference (ISI) and cross-talk between the sub-carriers(inter-carrier interference, ICI) arise. One possible way ofcounteracting the cross-talk between sub-carriers relates to usingorthogonal sub-carriers with separate frequencies. In general,inter-symbol interference can be entirely eliminated by adding to eachsymbol a protective time interval (guard period). The symbol iscyclically expanded in the guard period, to avoid any cross-talk betweenthe sub-carriers. If there is any cross-talk between the sub-carriers,this means that the sub-carriers are not orthogonal to each other.

The OFDM (Orthogonal Frequency Division Multiplex) method represents avariant of the multi-carrier method with orthogonal frequency-separatedsub-carriers. Inter-symbol interference is caused by multi-pathpropagation. In the case of OFDM-based data transmission in radiocommunication systems, an OFDM symbol is produced by the modulation ofuser data onto sub-carriers. This is effected by the application of theinverse fast-Fourier transform (IFFT) to the user data. Following this,either a cyclic prefix (CP) is added before each symbol or 0 data isappended to each symbol (zero padding, ZP). Successive OFDM symbols caninterfere as a result of multi-path propagation on the radio channel.

In order to retrieve the user data from the received data, the followingmethods can be used: in the case of CP, parts of the received symbol areignored, so that neighboring OFDM symbols are as interference-free aspossible. The fast-Fourier transform (FFT) is applied to the remainingdata for an OFDM symbol and this is then allocated to the relevantsub-carrier frequency as determined by the value of the transferfunction of the radio channel. By doing so, the user data can beretrieved.

The ZP case can be reduced to the CP case by appropriate addition of thereceived data, so that the data can be retrieved in the same way.Furthermore, in the ZP case the user data can be estimated by usingsuitable criteria—such as for example least squares (LS) or minimum meansquare error (MMSE)—to solve an overspecified system of equations.

The benefit of CP lies in the fact that neighboring OFDM symbols do notinterfere and there is no cross-talk between the sub-carriers if a longenough CP is chosen, that is at least as long as the maximum channeldelay (delay spread, DS). As in the case of CP or ZP, the insertion ofguard periods results in a reduction in the effective data transmissionrate for user data. Furthermore, in the case of CP a substantial part ofthe transmission capacity is used for transmitting a CP, which isespecially unwanted in mobile transmission methods. In radio systemsconforming to Hiperlan/2 (High Performance Radio Local Area Network Type2), the CP amounts to 20% of the time for an OFDM symbol.

As in the case of CP or ZP, the insertion of guard periods results in areduction in the effective data transmission rate for user data.Furthermore, in the case of CP a substantial part of the transmissioncapacity is used for transmitting a CP, which is especially unwanted inmobile transmission methods. In radio systems conforming to Hiperlan/2(High Performance Radio Local Area Network Type 2), the CP amounts to20% of the time for an OFDM symbol.

U.S. Pat. No. 6,345,076 B1 describes a method for the incoherent receiptof differentially modulated data. Symbols which are received areestimated using an incoherent MLSE (maximum likelihood sequenceestimation). For the purpose of improving the reception quality, thesymbols which are received are subdivided into overlapping symbolblocks, which overlap by at least one symbol. Because, in the case ofdifferentially modulated data, the items of data which are to betransmitted are not contained in the individual symbols but in the phasechanges of neighboring symbols, the overlapping of the symbol blocks isrequired so that there is a reference phase for each symbol in a symbolblock.

Hence, one possible object underlying the invention is to specify anadvantageous method for data estimation which makes possible thetransmission of data units without guard periods.

SUMMARY OF THE INVENTION

The inventors propose a method for estimating data units transmitted ina radio block via a radio channel, a signal sequence arising from thedata units which are transmitted is received in a receiving station. Thecomponents of the signal sequence which is received are assigned to atleast a first and a second signal block in the time-sequence of theirreceipt, and are processed block-by-block, with the signal blocksoverlapping in such a way that at least one component of the receivedsignal sequence belongs to both signal blocks, and by reference to thecomponents of both signal blocks estimated values are determined for thedata units which were transmitted. The use of overlapping signal blocksfor the estimation of the transmitted data units makes it possible toforgo a guard period signal blocks estimated values are determined forthe data units which were transmitted. The use of overlapping signalblocks for the estimation of the transmitted data units makes itpossible to forgo a guard period between individual data units. Inparticular, several radio blocks can be transmitted in succession withno guard periods, and can be analyzed, i.e. estimated, by the receivingstation.

It is advantageous if the overlap of the signal blocks is effected insuch a way that in each case there is at least one transmitted data unitfor which an estimated value can be determined by reference to bothsignal blocks. For this at least one transmitted data unit it ispossible to use, for example, an average of the estimated values, andthus to achieve improved estimation.

In a preferred development, after determination of the two estimatedvalues, the estimated value determined by reference to one of the twosignal blocks is used exclusively for the at least one transmitted dataunit. If one of the two estimated values is significantly worse than theother estimated value, that estimated value which has the largest erroris discarded. In this case, the choice of one of the two estimatedvalues permits a better estimate than would be possible, for example, byaveraging or by methods which supply only one estimated value for the atleast one transmitted data unit.

In one form of embodiment, a cyclic transfer matrix is assigned in eachcase to the signal blocks, and the estimated values are calculated bymultiplication of the signal blocks by the relevant inverse transfermatrix. The use of a cyclical transfer matrix or the relevant inversetransfer matrix enables a particularly simple calculation of theestimated values.

In an alternative form of embodiment, a transfer matrix with a Töplitzstructure and a band structure is assigned in each case to the signalblocks, and the estimated values are calculated by multiplication of thesignal blocks with the relevant pseudo-inverse transfer matrix. The useof a transfer matrix with a Töplitz structure and a band structure, orthe corresponding pseudo-inverse transfer matrix, as applicable, has theadvantage that the transfer matrix has full column rank, which thusensures that the pseudo-inverse transfer matrix always exists.Furthermore, with the use of a pseudo-inverse transfer matrix for thecalculation of the estimated values it is possible to achieve errorrates for the estimated values of the transmitted data units which arejust as low as for data transmissions in which guard periods areinserted in the familiar way between individual data units or individualradio blocks, as applicable. It is thus possible to achieve a higherdata transmission rate than with known systems but with no losses intransmission quality.

The inventors also propose a receiving station having all thecharacteristics necessary for carrying out the method.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of the present invention willbecome more apparent and more readily appreciated from the followingdescription of the preferred embodiments, taken in conjunction with theaccompanying drawings of which:

FIG. 1 shows a schematic data transmission from a transmitting to areceiving station,

FIG. 2 shows a first matrix representation of the estimation of data inaccordance with one embodiment of the invention,

FIG. 3 shows a second matrix representation of the estimation of data inaccordance with one embodiment of the invention,

FIG. 4 shows a third matrix representation of the estimation of data inaccordance with one embodiment of the invention,

FIG. 5 shows block error rates as a function of the signal-to-noiseratio for data estimates made in accordance with one embodiment of theinvention, using various parameters.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings, wherein like reference numerals refer to like elementsthroughout.

In these figures, identical items are given the same referencecharacters.

A receiving station is any station which can receive signals. In whatfollows a base station is regarded as a receiving station. A receivingstation can also be a mobile station. A mobile station is, for example,a mobile telephone or even a device for the transmission of image and/orsound data, for sending faxes, Short Message Service (SMS) messages ande-mails, and for accessing the Internet, which can be moved from onelocation to another. It is thus a general receiving unit in a radiocommunication system.

The Method and receiving station can be used to advantage in anyarbitrary radio communication systems. The term radio communicationsystems is to be taken as any arbitrary system in which datatransmission is effected between stations via a radio interface. Thedata can be transmitted either bi-directionally or uni-directionally.Radio communication system are, in particular, mobile radio systemsconforming for example to the GSM (Global System for MobileCommunication) or UTMS (Universal Mobile Telecommunication System)standards. Future mobile radio systems, for example fourth generationand multiple carrier systems using an OFDM method or single carriersystems using a cyclic prefix (CP) or 0-data (ZP), are also to beconsidered as radio communication systems.

FIG. 1 shows in schematic form a data transmission from a transmittingstation MS to a receiving station BS. The transmitting station MStransmits a radio block d, which has eight data units d11, d12, d13,d14, d21, d22, d23, d24, over a radio channel to the receiving stationBS. Due to multi-path propagation, for example via the three paths W1,W2, W3, the receiving station BS receives a signal sequence S having tencomponents K1, K2, K3, K4, K5, K6, K7, K8, K9, K10. The receivingstation BS has a transmit and receive unit SE together with an analysisunit P for storing the signal sequence S which it has received and forestimating the data units d11, d12, d13, d14, d21, d22, d23, d24 whichwere transmitted. The radio channel can be specified by a channel pulseresponse h, having in this example the three components h1, h2, h3, i.e.it has a length L=3. Here, the length L=3 means that the data unit d11which is the first to be sent interferes with the following two dataunits which are transmitted, due to multi-path propagation. The effectof the radio channel on the transmission of the radio block d can bedescribed mathematically by a system matrix H determined by the channelpulse response h.

FIG. 2 shows a matrix representation of the data transmission from thetransmitting station BS to the receiving station BS. The signal sequenceS which is received can be expressed as the product of the system matrixH and the radio block d. The components K1, K2, K3, K4, K5, K6, K7, K8,K9, K10 of the signal sequence S contain the effects of interferencebetween the transmitted data units d11, d12, d13, d14, d21, d22, d23,d24. The time sequence of the receipt of the components K1, K2, K3, K4,K5, K6, K7, K8, K9, K10 of the signal sequence S corresponds to theirnumbering from one to ten.

For the purpose of estimating the data units d11, d12, d13, d14, d21,d22, d23, d24 which have been transmitted, the receiving station BSforms a first signal block X1 using the components X11, X12, X13, X14,X15, X16 from the first six components K1, K2, K3, K4, K5, K6 of thesignal sequence S, and second signal block X2 using the components X21,X22, X23, X24, X25, X26 from the last six components K5, K6, K7, K8, K9,K10 of the signal sequence S. The last two components X15, X16 of thefirst signal block X1 then correspond to the first two components X21,X22 of the second signal block X2, i.e. X15=X21 and X16=X22. A transfermatrix H1, H2 is assigned to each of the two signal blocks X1, X2. Themultiplication of the relevant transfer matrix H1, H2 by the first orthe second transmission block d1, d2 of the data units d11, d12, d13,d14, d21, d22, d23, d24 which have been transmitted gives in each casethe first and the second signal block X1, X2 respectively, ignoring theinterference between the two transmission blocks d1, d2. The firsttransmission block d1 has the first four data units d11, d12, d13, d14in the radio block d, and the second transmission block d2 has the lastfour data units d21, d22, d23, d24 in the radio block d.

The naming of the components in the transmission blocks and the signalblocks has been chosen so that the first number permits its assignmentto the appropriate block, while the second number specifies its positionwithin the block. X13 is thus the third component X13 of the firstsignal block X1.

Both the system matrix H and also the transfer matrices H1, H2 have aTöplitz structure and band structure, i.e. they have full column rankand a pseudo-inverse transfer matrix always exists for these transfermatrices. A matrix has a band structure if a triangular portion of it onthe top right and a triangular portion of it on the bottom left containonly zeros. A matrix has a Töplitz structure if all the componentswithin the diagonals have the same value.

The receiving station BS now estimates the data units d11, d12, d13, d14which were transmitted in the first transmission block d1 by multiplyingthe first signal block X1 by the pseudo-inverse transfer matrix H1# ofthe first transfer matrix H1. In a similar fashion, the data units d21,d22, d23, d24 which were transmitted in the second transmission block d2are estimated by multiplying the second signal block X2 by thepseudo-inverse transfer matrix H2# of the second transfer matrix H2.Then: H1#*X1=d1′ and H2#*X2=d2′. Here, d1′ and d2′ are the estimatedtransmission blocks d1′ and d2′, i.e. the estimated values for thetransmitted data units d11, d12, d13, d14, d21, d22, d23, d24 of theradio block d.

The method makes it possible to omit guard periods in systems whichuntil now have used guard periods between transmission blocks, such asfor example OFDM systems or block-based individual carrier systems witha cyclic prefix (CP) or 0-data (ZP), as applicable. In the exemplaryembodiment described for FIG. 2, interference between the twotransmission blocks d1, d2 does indeed increase because a guard intervalhas been omitted, but the transmission capacity, i.e. the datatransmission rate, is increased.

In order, furthermore, to eliminate the effects of interference betweenthe transmission blocks d1, d2 which are transmitted as one radio blockd, i.e. without guard periods, when estimating the data units d11, d12,d13, d14, d21, d22, d23, d24 which have been transmitted, a specialformation of the signal blocks is used in a form of embodiment as shownin FIG. 3.

FIG. 3 shows in schematic form the special formation of the signalblocks which enables an estimate to be made, of the data units d11, d12,d13, d14, d21, d22, d23, d24 which were transmitted, which has errorrates such as have until now only been achieved with the use of guardperiods.

The radio block d, which has already been described for FIGS. 1 and 2,is transmitted over the same radio channel with the channel pulseresponse h with its length of L=3, and leads in turn to the receipt of asignal sequence S.

For the purpose of estimating the data units d11, d12, d13, d14, d21,d22, d23, d24 transmitted in the radio block d, three signal blocks X1,X2, X3 are now formed. The first two signal blocks X1, X2 are the samesignal blocks X1, X2 as already described for FIG. 1. The third signalblock X3 with its components X31, X32, X33, X34, X35, X36 is formed fromthe second to the eighth components K2, K3, K4, K5, K6, K7, K8 of thesignal sequence S, and thus matches the last four components X13, X14,X15, X16 of the first signal block X1 and the first four components X21,X22, X23, X24 of the second signal block X2. Consequently: X31=X13,X32=X14, X33=X15=X21, X34=X16=X22, X35=X23 and X36=X24.

This formation of the signal blocks X1, X2, X3 can be represented asthree overlapping transmission blocks d1, d2, d3, to each of which isassigned a transfer matrix H1, H2, H3. These virtual transmission blocksare not transmitted, but are used in describing the method. The radioblock d is what is transmitted.

To the first and second signal blocks X1, X2 are assigned the transfermatrices H1, H2 previously described. The third signal block X3 has athird transfer matrix H3, which overlaps the first and second transfermatrices H1, H2.

For each transfer matrix H1, H2, H3 the receiving station BS now formsthe associated pseudo-inverse transfer matrix H1#, H2#, H3# andmultiplies this by the corresponding signal block X1, X2, X3. From thefirst signal block X1 is derived a first estimated transmission blockd1′ with estimated values for the first four data units d11, d12, d13,d14 which were transmitted in the radio block d. The second signal blockX2 provides a second estimated transmission block d2′ with estimatedvalues for the last four data units which were transmitted, d21, d22,d23, d24. The third signal block X3 gives a third estimated signal blockd3′ with estimated values for the third to the sixth data units whichwere transmitted, d13, d14, d21, d22, i.e. for the last data units d13,d14 which were transmitted in the first transmission block d1 and forthe first two data units d21, d22 which were transmitted in the secondtransmission block d2. Due to the interference effects between the dataunits in the transmission blocks d1, d2, d3, the first and lastestimated values of the data units transmitted for the transmissionblocks d1, d2, d3 exhibit the largest errors. For the first transmissionblock d1, these are the components d11 and d14, for the secondtransmission block d2 they are the components d21 and d24, and for thethird transmission block X3 the components d13 and d22. Consequently,the best estimate of the transmitted data units d1, d12, d13, d14, d21,d22, d23, d24 is obtained if the estimated values with the largesterrors are not used. Hence, for the first three data units transmitted,d11, d12, d13, the estimated values used are those which have beendetermined by reference to the first signal block X1. The fourth andfifth data units transmitted, d14, d21, are determined by reference tothe third signal block X3, while the sixth to eighth data unitstransmitted, d22, d23, d24, are determined by reference to the secondsignal block X2. It is particularly advantageous if other radio blocksare transmitted continuously before and after the radio block d. It ispossible in this way to form further signal blocks which overlaprespectively with the first or the second signal blocks, X1, X2 in thesame way as does the signal block X3. The first and the last data unitstransmitted, d11, d24, can then be estimated using those additionalsignal blocks which overlap respectively with the first and the secondsignal blocks, X1, X2. The result of doing so is an improved estimatefor the first and the last data units transmitted, d11, d24.

With a continuous data transmission it is possible, i.e. by the use, asapplicable, of overlapping signal blocks or overlapping transfermatrices or overlapping (virtual) transmission blocks, to estimate allthe data units transmitted just as well as has until now been possibleonly by the use of guard periods between the data units transmitted orbetween (real) transmission blocks or between radio blocks, asapplicable.

It is, of course, also possible to form larger signal blocks with morethan six components, for example with 32 or 64, or the overlap of thesignal blocks can be larger than four components, as appropriate.Furthermore, there can be other channel pulse responses, with lengthsgreater than three. Even under transmission conditions which differ inthese ways, the method can be applied in the same way.

Instead of assigning transfer matrices with Töplitz structures and bandstructures, it is also possible to assign cyclic transfer matrices tothe overlapping signal blocks. With these, the calculation is easierthan with Töplitz transfer matrices, but with Töplitz transfer matricesit is possible to achieve lower error rates than with cyclic transfermatrices.

FIG. 4 shows the assignment of cyclic transfer matrices C1, C2, C3 tocorresponding overlapping signal blocks Y1, Y2, Y3 for the transmissionof the radio block d from FIG. 2 or FIG. 3, as applicable. A firstsignal block Y1 with the components Y11, Y12, Y13, Y14 has the firstfour components K1, K2, K3, K4 of the signal sequence S. A second signalblock Y2 with the components Y21, Y22, Y23, Y24 has the fifth to theeighth components K5, K6, M7, M8 of the signal sequence S, while a thirdsignal block Y3 with the components Y31, Y32, Y33, Y34 has the third tothe sixth components K3, K4, K5, K6 of the signal sequence S. Then:Y13=Y31, Y14=Y32, Y21=Y33 and Y22=Y34. The last two components K9, K10of the signal sequence S are not used until a signal block, whichoverlaps with the second signal block Y2, is formed for a further radioblock transmitted immediately after the radio block d. The estimation ofthe transmitted data units d11, d12, d13, d14, d21, d22, d23, d24 iseffected in the same way as described for FIG. 3. The sole difference isthat the cyclic transfer matrices C1, C2, C3 are quadratic, andconsequently have inverse transfer matrices C1 ⁻¹, C2 ⁻¹, C3 ⁻¹ insteadof pseudo-inverse transfer matrices. Then: C1 ⁻¹*Y1=d1′, C2 ⁻¹*Y2=d2′and C3 ⁻¹*Y3=d3′.

FIG. 5 shows block error rates (BER) for estimated data units as afunction of the signal-to-noise ratio (SNR). Pseudo-inverse and inversematrices were used, together with various signal block sizes and variousoverlaps between the signal blocks, i.e. between the transfer matricesor the corresponding transmission blocks, as applicable. Here, CMIstands for an inverse cyclic transfer matrix and PI for a pseudo-inversetransfer matrix. The other numbers on each line give, from left toright, the size of the signal blocks together with the number ofestimated values of transmitted data units, at the beginning and at theend of an estimated transmission block, which are discarded, i.e. arenot used. The detection error for the transmitted data units arises bothfrom the interference effects between data units induced by multi-pathpropagation and also from noise in the radio channel, for example due todata transmissions from other transmitting stations.

The invention has been described in detail with particular reference topreferred embodiments thereof and examples, but it will be understoodthat variations and modifications can be effected within the spirit andscope of the invention covered by the claims which may include thephrase “at least one of A, B and C” as an alternative expression thatmeans one or more of A, B and C may be used, contrary to the holding inSuperguide v. DIRECTV, 69 USPQ2d 1865 (Fed. Cir. 2004).

1. Method for estimating data units (d11, d12, d13, d14, d21, d22, d23,d24) transmitted via a radio channel in a radio block (d), by which thetransmitted data units (d11, d12, d13, d14, d21, d22, d23, d24) cause asignal sequence (S) to be received in a receiving station (BS), thecomponents (K1, K2, K3, K4, K5, K6, K7, K8, K9, K10) of the receivedsignal sequence (S) are assigned in the time-sequence of their receiptto at least a first signal block and a second signal block (X1, X2, X3;Y1, Y2, Y3) and are processed block by block, whereby the signal blocks(X1, X2, X3; Y1, Y2, Y3) overlap in such a way that at least onecomponent (K3, K4, K5, K6, K7, K8) of the received signal sequence (S)belongs to both signal blocks (X1, X2, X3; Y1, Y2, Y3), and, byreference to the components of both signal blocks (X1, X2, X3; Y1, Y2,Y3), estimated values are determined for the data units (d11, d12, d13,d14, d21, d22, d23, d24) which were transmitted.
 2. Method in accordancewith claim 1, in which the overlapping of the signal blocks (X1, X2, X3;Y1, Y2, Y3) is effected in such a way that there is at least one of thedata units (d13, d14, d21, d22) which was transmitted for whichestimated values are determined by reference to each of the two signalblocks (X1, X2, X3; Y1, Y2, Y3).
 3. Method in accordance with claim 2,in which after both the estimated values have been determined, theestimated value determined by reference to one of the two signal blocks(d1, d2, d3) is used exclusively for the at least one data unit (d13,d14, d21, d22) which was transmitted.
 4. Method in accordance with claim1, 2 or 3 in which a cyclic transfer matrix (C1, C2, C3) is assigned toeach of the signal blocks (Y1, Y2, Y3), and the estimated values arecalculated by multiplying the signal blocks (Y1, Y2, Y3) by the relevantinverse transfer matrix.
 5. Method in accordance with claim 1, 2 or 3 inwhich a transfer matrix (H1, H2, H3) with a Töplitz structure and bandstructure is assigned to each of the signal blocks (X1, X2, X3), and theestimated values are calculated by multiplying the signal blocks (X1,X2, X3) by the relevant pseudo-inverse transfer matrix.
 6. Receivingstation (BS) with facilities (SE) for receiving a signal sequence (S)arising from data units (d11, d12, d13, d14, d21, d22, d23, d24)transmitted in a radio block (d), facilities (P) for assigning thecomponents (K1, K2, K3, K4, K5, K6, K7, k8, k9, K10) of the receivedsignal sequence (S) in the time-sequence of their receipt to at least afirst signal block and a second signal block (X1, X2, X3), and withfacilities (P) for processing the signal blocks (X1, X2, X3) block byblock, whereby the signal blocks (X1, X2, X3) overlap in such a way thatat least one component (K3, K4, K5, K6, K7, K8) of the received signalsequence belongs to both signal blocks (X1, X2, X3), and facilities (P)for determining, by reference to the components of both signal blocks(X1, X2, X3), estimated values for the data units (d11, d12, d13, d14,d21, d22, d23, d24) transmitted.